This bearing allows the upper spring seat of the front strut assemblies to rotate when you turn the steering wheel. If the strut bearing is ceased, the upper spring seat will not be able to rotate and the spring will twist instead, which can cause damage to the spring over time or even force the spring out of the seat. The more noticeable signs of a bad strut bearing typically include excess noise or resistance in the steering wheel while turning or intermittent knocking when going over bumps. The steering wheel may also "jump" back after making a turn. Since these are sealed bearings, the best way to prevent them from failing is to simply replace them along with the front struts. Sold individually, one required per front strut assembly (2 per car).